Please note that this tagging variant is not the mostly used one, the more commonly used method is described here source:maxspeed=* and has different values for implicit maxspeeds according to the context you are driving in (urban / rural / motorway). Please consider using the more diffuse method in order to avoid fragmentation. It is also important to know that the way to tag maxspeed here (maxspeed=IT:urban etc.) will not be correctly evaluated by most current software.

This means the corresponding maxspeed=* is not set by special speed limit sign, but by the area the road is in.
The maxspeed value contains a string and not a number.